1. Field of the Invention
The present invention relates to a zoom lens and, more particularly, to a zoom lens used for, for example, a digital camera using a CCD.
2. Description of the Prior Art
Conventionally, as zoom lenses in this field, the zoom lenses disclosed in Japanese Unexamined Patent Publication Nos. 2002-244039 and 2002-006216 have been available.
Japanese Unexamined Patent Publication No. 2002-244039 discloses a zoom lens in which a first lens group having a positive focal length, a second lens group having a negative focal length, and third, fourth, and fifth lens groups each having a positive focal length are arranged from the object side toward the image side, and an aperture stop is provided near the third lens group. In this embodiment, the number of lenses is 11 or 12, the zoom ratio is about 4.7, and the field angle at the wide angle end is about 66°.
Japanese Unexamined Patent Publication No. 2002-006216 discloses a zoom lens in which a first lens group having a positive focal length, a second lens group having a negative focal length, a third lens group having a positive focal length, and a fourth lens group having a positive focal length are arranged from the object side toward the image side. In this embodiment, the number of lenses is 11 the zoom ratio is about 4.9, and the field angle at the wide angle end is about 60°.
In the field of cameras, as well, including, for example, digital cameras and video cameras which use CCDs (Charge Coupled Devices) and CMOSs (Complementary Metal Oxide Semiconductors), there have recently been increasing demands for compact, low-cost zoom lenses having high zoom ratios and wide field angles.
In order to meet these demands, however, an overall lens system needs to be comprised of the minimum number of lenses even though a high zoom ratio and a wide field angle at the wide angle end are required. In addition, an optimal zoom lens type, a proper lens arrangement, a proper lens power distribution, and the like must be selected.
From this point of view, the zoom lens disclosed in Japanese Unexamined Patent Publication No. 2002-244039 has a complicated structure, that is, has a five lens group construction even for a zoom ratio of about 5.
Although the zoom lens disclosed in Japanese Unexamined Patent Publication No. 2002-006216 has a four group lens construction with a zoom ratio of about 5, the number of lenses is as large as 11 or more. In this embodiment, the number of lenses of the first lens group is three, and the number of lenses of the fourth lens group is two or three. As described above, for example, too many lenses makes it difficult to achieve reductions in size and cost.